annotate .clang-format @ 49879:dd804d83822c

setup: drop legacy osx compiler tuning to enable universal builds

This was triggering deprecation warnings about migrating to `packaging.version`
from `distutils` Version classes with `make local`.  But rather than migrate
that code, let's just get rid of some ~10-12 year old workarounds.  As a bonus,
the cext libraries that are built are now universal binaries containing x86_64
and arm64 images (at least when built on macOS 11.4 with Xcode 12.5 and the
universal version of Python 3.9.13).

Several things to note here:

   - Apple dropped support for 10.15 in Nov 2022, and OS X Lion that is
     referenced is 10.7 (unsupported since late 2014)
   - `xcode4` was basically always True because of the `>=` check (10.8 used
     Xcode 5, and I have Xcode 10.2 on 10.14)
   - `xcode51` was always False for modern-ish Xcode, because of the exact
     version string matching
   - Python 3.8 only supports OS X 10.9+; the Python 3.9.1+ universal installer
     is macOS 11+ only, and Python 3.10 drops the x86_64 installer to deliver
     only the universal installer.

All of this is to say, the only thing lost by dropping this code on modern Xcode
is that `os.environ['ARCHFLAGS'] = ''` is no longer set.  But we probably
shouldn't be setting that anymore, as shown by the universal libraries now being
generated.  I was able to `make local` and `python3 run-tests.py --local` with
python 3.9.9, Xcode 10.2, and macOS 10.14.6, and didn't incur any more than the
usual few test errors, so this should still work on some older versions of
macOS.

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